Exhaust aftertreatment systems, particularly vehicular systems, increasingly make use of hydrocarbon injection for treatment of various exhaust constituents of the exhaust gas flow. For example, vehicles equipped with diesel engines typically include exhaust systems that may have diesel particulate filters for removing particulate matter from the exhaust stream. With use, soot or other carbon-based particulate matter (PM) accumulates on the diesel particulate filters. To prevent diesel particulate filters from becoming excessively loaded, they are periodically regenerated by burning off (i.e., oxidizing) the particulates that accumulate on the filters. One approach for regeneration is to inject HC (e.g., fuel) into the exhaust gas flow for combustion, such as by the use of an oxidation catalyst, to raise the temperature of the exhaust and promote combustion of the accumulated PM in the filter.
In addition to particulate filters for removing PM, exhaust systems can be equipped with catalytic devices for removing or controlling other undesirable emission constituents, such as carbon monoxide (CO) and nitrogen oxides (NOx). Catalytic devices such as lean NOx catalysts, selective catalytic reduction (SCR) catalysts and lean NOx traps. These devices also may make use of HC injection, either to promote the catalytic reaction or to regenerate the catalyst material.
HC can be provided by controlling the combustion process so that unburned HC remains post-combustion in the exhaust gas flow. HC can also be provided by injecting HC directly into the exhaust aftertreatment system, such as by using a fuel injector that is operably attached to the fuel tank through various fuel conduits. While direct injection has been used for this purpose, its usefulness has been limited by the ability to provide low cost injectors that atomize the fuel sufficiently for evaporation and combustion in the exhaust aftertreatment system and that are also resistant to clogging or plugging by PM and other constituents found in the exhaust gas flow. Insufficient atomization of the HC can result in incomplete combustion or conversion by the exhaust treatment devices that allows the HC to slip through the system and be released to the external environment. HC slip also reduces the overall fuel efficiency of the engine, and in vehicular application, the efficiency of the vehicle.
Accordingly, it is desirable to provide fuel injectors that improve fuel atomization, reduce HC slip and improve engine and vehicle fuel efficiency.